The invention relates to a rotary-piston engine comprising at least two two-armed rotary pistons, which are located in an essentially spherical housing and which rotate in common about a rotational axis running through the center of said housing. Each of the rotary pistons comprises two pistons in the form of piston arms that are interconnected in a fixed manner, lie essentially diametrically opposite to each other with respect to the center of the housing and execute pivoting displacements back and forth in opposite directions about a pivoting axis running perpendicular to the rotational axis, during their rotation, whereby guide members are embodied on at least two pistons, which engage in at least one guide groove embodied in the housing for controlling the pivoting displacements.
Furthermore, the invention pertains to a vehicle with such a rotary-piston engine.
Rotary piston-engines belong to the category of combustion engines, where the operating cycles of embedding, compressing, expanding, and emitting of the combustion gas mixture is effected according to the four-stroke Otto or diesel method with externally-supplied ignition or self-ignition by means of pivoting movements of the pistons between two end positions.
A rotary piston-engine of the above-mentioned type known from WO 03/067033 A1 comprises two rotary pistons rotating in a housing which is spherical on the inside, the rotary pistons each being supported on a journal forming the pivoting axis via a bearing ring being connected with their pistons and sealed against the housing. The journal is fixedly connected with a shaft, which forms the rotational axis. The pistons of the rotary pistons located opposite to one another each have a sliding surface facing towards the housing, an operating side with an operating surface, and a backside facing away therefrom, whereby two operating sides of two adjacent pistons facing one another define an operating chamber together with the housing, and the backsides of two adjacent pistons define an antechamber together with the housing, the antechamber increasing or decreasing in volume in opposite direction to the operating chambers.
The back and forth pivoting movements of the pistons are bilaterally guided in a groove arranged on the inside of the spherical housing by means of guide members, the guide members being described as piston-solid roller journals or slide bearings. The geometry of this groove acting as a control cam has the shape of a circle constricted on diametrically opposite sides. This roller journal or slide-bearing guide positioned in the piston has the disadvantage that, due to the tangential orientation of the guide members, two staggered rollers are necessary so that during a change of the guide force onto the opposite side, a grinding does not take place on the groove, caused by the reversal of the unrolling direction of rotation. A slide bearing, in turn, causes high friction and thus reduced efficiency and high wear and tear on this most important part of the engine kinematics, which replaces the crankshaft of the lifting cylinder motor.
A further disadvantage of this guide configuration is seen in that the roller journals are mounted on the piston backsides, protruding beyond them, and that the guide grooves at the housing side, which work as antechamber walls for a pre-compression, are not covered against the piston backsides. The pre-compression is thus considerably reduced by this fluidic dead space. Furthermore, the lubricating fluid necessary for the lubrication of the rollers and guide grooves can reach through overflow channels into the operating chamber partly as leakage fluid and can lead to a high consumption of lubricating fluid as well as to two-stroke-like blue-smoke in the exhaust gas, whereby it is difficult to fulfill today's motor vehicle exhaust gas standards and it becomes difficult or impossible to use the rotary-piston engine several times.
With the known rotary-piston engine, a perfect mass equilibrium as well as moment distribution is achieved by the symmetrical piston movements. However, because the pivoting movements of the piston halves are three-dimensional movements, equalized masses and moments are not sufficient here for a quiet run, contrary to lifting cylinder and/or rotary engines. The piston and guide member masses dislodge and approach the rotational axis in a 90° cycle. Related thereto are rotary mass changes leading to free Coriolis forces, which cause corresponding torque fluctuations on the rotational axis. Due to the fact that the torque fluctuations are additionally in phase therewith by means of operating cycle and compression, an extensive damping of these torsional vibrations, for example by means of torsional vibration dampers in the output, high gyrating masses and/or a second engine coupled to the rotational shaft phase-shifted at 90° , as well as all-around elastomer suspension, must take place for a quiet engine run.
In the known rotary-piston engine, the pivoting of the pistons takes place such that, during a 360° rotation about the rotational axis, the 4 cycles of the suction, compression, expansion, and discharge result for both operating chambers being defined between the pistons. Thus, a self-ignition or externally supplied ignition thus takes place every 180° . Furthermore, the two antechambers formed by the piston backsides are used for pre-compression of the fresh mixture (gas) and for charging the operating chambers, whereby one respective operating chamber is charged by both antechambers. For controlling this gas exchange, a relatively complex valve configuration is provided, which comprises check valves for controlling during suction into the antechambers and either a magnetic valve, which controls bypasses located outside of the housing, or check valves in the piston walls with a direct pass from the antechambers into the operating chambers.
The spherical motor housing yields the largest room content at a minimal outer surface. This means that with an air or fluid cooling of the outer surfaces, in comparison with a lifting cylinder or rotary engine, a considerably smaller amount of cooling surface must be available for a corresponding engine output. In particular, when using the high power spectrum made possible by the geometry of the sphere, an interior cooling must therefore additionally be present. With the known rotary-piston engine, it is provided to essentially ensure this interior cooling with the fresh mixture, which cools the antechamber side of the pistons and is to be preheated thereby. It is considered disadvantageous that a preheating of the fresh mixture can lead to power loss and knocking problems and is only suitable for a small power density.